Plate heat exchanger and end plate associated therewith

ABSTRACT

A plate heat exchanger has two end plates, at least one of which is provided with a number of port openings ( 11 ) to allow inflow and outflow of a number of heat exchanging fluids, and a number of heat transfer plates located between the end plates. One of the end plates ( 1 ) has two individual segments ( 10 ) that are relatively displaceable in the plane of the end plate.

FIELD OF THE INVENTION

The present invention relates to a plate heat exchanger comprising twoend plates, at least one of which is provided with a number of portopenings to allow inflow and outflow of a number of heat exchangingfluids, and a number of heat transfer plates located between the endplates. The invention also relates to an end plate that is intended tobe included in a plate heat exchanger.

BACKGROUND ART

A conventional plate heat exchanger is made up of a frame which supportstwo flexurally rigid clamping plates and a pack of heat transfer platesarranged between said plates. The two plates of the frame comprise apressure plate, which is movable during assembly, and a frame plate,which is fixed during assembly, said plates being pulled together bymeans of bolts, thereby clamping the heat transfer plates. For the sakeof simplicity, the pressure plate and the frame plate will both bereferred to as end plates below. The number of heat transfer plates aswell as their size is determined by the field of use of the plate heatexchanger. One of the end plates, or both, is provided with through portopenings to allow inflow and outflow of a number of (usually two) heatexchanging fluids. The heat transfer plates are, in turn, provided witha number of through ports, which form a first inlet channel and a firstoutlet channel for a first fluid through the plate pack and a secondinlet channel and a second outlet channel for a second fluid through theplate pack. These channels extending through the plate pack communicatewith the through port openings of the end plates.

The heat exchanging fluids flow separately through the plate heatexchanger in different plate interspaces formed between the heattransfer plates. In most cases, every second such plate interspacecommunicates with the first inlet and outlet channel, each plateinterspace being adapted to define a flow area and to conduct the firstheat exchanging fluid between said inlet and outlet channels.Correspondingly, the other plate interspaces communicate with the secondinlet and outlet channel for a flow of the second heat exchanging fluid.Fluid-tight sealing means such as a gasket or weld are provided roundthe through ports of the heat transfer plates. The sealing means arearranged round some of the ports alternatingly in every second plateinterspace and, in the other plate interspaces, round the other ports soas to form the two separate channels for the first heat exchanging fluidand the second heat exchanging fluid, respectively.

Since the purpose of a plate heat exchanger is to achieve a heatexchange between two fluids, both the end plates and the heat transferplates are subjected to a significant influence of temperature. Thisinfluence causes problems, as will be described below.

The heat transfer plates are usually relatively thin and are in directcontact with the heat exchanging fluids. The temperature of the fluidswill thus directly affect the temperature of the heat transfer plates,the length of which will change to a certain extent depending on thecoefficient of linear expansion of the plate material.

The end plates, which are located on either side of the pack of heattransfer plates, are considerably thicker than the heat transfer plates.Moreover, the end plates do not enter into direct contact with the heatexchanging fluids as do the heat transfer plates. However, thetemperature of the end plates will be affected on one side of the endplate by the environment surrounding the plate heat exchanger and, onthe other side, by the temperature of the respective outermost heattransfer plates in the plate pack.

The changes in length will vary due to the difference in the influenceof temperature between the end plates and the heat transfer plates incombination with different plate thickness. In addition, the differentlength changes of the end plates and heat transfer plates may bereinforced by the fact that the plates are often made of differentmaterials having, thus, different coefficients of linear expansion. Thedifferent length changes of the plates result in high tensions in theattachment of the connections between the end plates and the heattransfer plates, which leads to an increased risk of fatigue damage.

However, the primary cause of fatigue damage is the difference inthermal inertia between the end plates and the heat transfer plates. Arapid change in the temperature of the fluids will cause the temperatureof the heat transfer plate to change immediately whereas the temperatureof the end plate will change very slowly. In many processes, temperaturevariations occur during operation, for example in batch processes. Inbatch processes, a certain amount of components, such as fluids, powderor pellets, is processed for a certain period of time, following whichthe process is interrupted to allow emptying, cleaning and charging of anew batch. Thus, a batch process involves many starts and stops inconnection with which the temperature changes from a maximum value to aminimum value.

Fatigue damage in the attachment of the connections between the endplates and the heat transfer plates is due to a number of factors andmay lead to fracture in the material and thus to a shortened servicelife of the plate heat exchanger.

To compensate for the different changes in length of the end plates andthe heat transfer plates, it is proposed in U.S. Pat. No. 6,119,766 toarrange one or more bellows on the plate heat exchanger. The bellows areconnected to an end plate provided with port openings and to theassociated outer heat transfer plate and are adapted to absorb anymovements between the frame and the pack of heat transfer plates.

However, there are several fields of application in which a plate heatexchanger provided with bellows as described above cannot be used. Forexample, the bellows design does not allow high pressures to be used inthe plate heat exchanger. To withstand high pressures, in the range of100–150 bars (10–15 Mpa), the thickness of the material of which thebellows are made must be great, which means that the bellows will berigid. However, such a rigid design means that the bellows lose theirflexibility and thus their capacity to absorb movement between the endplates and the heat transfer plates in a satisfactory manner.

Furthermore, a plate heat exchanger provided with a bellows cannot beused, for example, in certain types of chemical applications wherespecific materials that are resistant to chemical attack must be used.In most cases, no such bellows are available since different kinds ofceramic materials are often used to obtain the chemical durability.Ceramic materials are usually brittle and cannot be used in bellows ofthe kind described in U.S. Pat. No. 6,119,766.

JP 2000 329493 discloses a plate heat exchanger comprising an end plateprovided with slits. The slits are adapted to absorb small deformationswhen a thermal stress is applied to both the inlet and the outlet holeson the end plate. The end plate, which for reasons related tomanufacture, no doubt, is made in one piece, is provided with twoparallel slits. The slits extend from the opposite longitudinal edgesacross the main portion of the width of the end plate adjacent to theoutlet/inlet holes.

The design of the slits in JP 2000 329493 allows only small deformationsof about 1/100 mm to be absorbed. Larger deformations will cause cracksto appear at the extreme ends of the slits and the end plate will thusbe damaged.

Accordingly, the plate heat exchanger design described in JP 2000 329493cannot be used in large plate heat exchangers, in which the thermaldeformations may be several millimetres.

Various designs of plate heat exchangers and of parts included thereinhave been known for a long time. One example is EP 033,201, whichdiscloses a frame for a plate heat exchanger. In conventional manner,the frame is made up of two end plates, which however in turn aredivided into a number of units. The purpose of this division of the endplates into units is on the one hand to allow simpler and more rationalmanufacturing and, on the other hand, to facilitate the handling andassembly of the end plates and the plate heat exchanger. In order toserve as conventional end plates, the different units are assembled intorigid plates in connection with the assembly of the plate heatexchanger.

Thus, there is currently no plate heat exchanger concept in which theplate pack is clamped between two end plates and which can be used in asatisfactory manner under the conditions described above, for example athigh pressures and in a chemically aggressive environment, and which canabsorb considerable thermal deformations.

SUMMARY OF THE INVENTION

One object of the invention is therefore to provide a plate heatexchanger which solves or at least alleviates the above problems. Thepurpose is to provide a plate heat exchanger with a simple constructionthat in a satisfactory manner can be used under different conditions,for example at high pressures and in chemically aggressive environments,and which is capable of absorbing thermal deformations. Further objectsand advantages of the invention will be apparent from the followingdescription.

The objects of the invention have been achieved by a plate heatexchanger of the type mentioned by way of introduction, which ischaracterised in that one of the end plates comprises two individualsegments that are relatively displaceable in the plane of the end plate.In the event of a change in length and width in the heat transfer platesthat does not occur as rapidly in the end plates or is non-existent inthese plates, the segments of the end plate are thus able to move indifferent directions in the plane of the end plate. Consequently, thedisplaceable segments of the end plate can compensate for the lengthchanges in the heat transfer plates, and the stress in the attachmentsof the connections between the port openings of the end plates and theinlet and outlet channels formed through the pack of heat transferplates is thus reduced. Furthermore, the plate heat exchanger does notcomprise any components that prevent use at high temperatures and inchemically aggressive environments. Accordingly, the inventiveconstruction of the plate heat exchanger provides a solution to theabove problems.

Preferred embodiments of the plate heat exchanger are defined independent claims 2–9.

According to a preferred embodiment, each segment of the end platecomprises a port opening. Compensation, as described above, for varyinglength changes in the end plates and the heat transfer plates can thusbe achieved at each connection between the port openings of the endplates and the channels formed through the heat transfer plates. Thismeans that each attachment of connections is exposed to the leastpossible stress and that the fatigue damage can be further reduced.

According to another preferred embodiment, said port openings arepositioned on the end plate along the same geometric centre line. Thispositioning of the port openings is advantageous from the point of viewof manufacture, for example in that it allows a narrow end plate and,thus, a narrow plate heat exchanger to be obtained. This design of theend plate permits a similar design of the heat transfer plates, whichare thus allowed to be mixed with each other by rotating them abouttheir longitudinal axis. This is preferred from the point of view ofmanufacture since only one embodiment of the heat transfer plate isneeded in the plate heat exchanger.

Segmenting such an end plate, on which the port openings are positionedalong a geometric centre line is advantageous. Due to its shape, thelong and narrow end plate is subjected to considerable length changes inconnection with temperature variations, and these changes are thuscompensated for by the segmentation.

According to yet another preferred embodiment, a surface with increasedfriction is arranged on at least one of the segments of the end plateand/or on an adjacent plate. Said adjacent plate may be either theoutermost plate of the pack of heat transfer plates or a plate arrangedbetween the end plates and the pack of heat transfer plates. Due to thefriction, a flexibility is obtained between the end plate and saidadjacent plate when length changes occur in the plates. The stress onthe connections between the plates is thereby reduced.

According to a preferred embodiment, said increased friction is obtainedby providing at least one of the segments round a port opening of theend plate with a fixing pattern for engagement with the adjoining plate.The engagement thus enhances the flexibility between the plates.

The flexibility between the end plates and the pack of heat transferplates may be further enhanced if the plate adjoining the end plate isprovided with a fixing pattern corresponding to that of the end plate.

According to another preferred embodiment, a sliding element is arrangedbetween the heat transfer plates and the adjoining end plate. Despitethe above-mentioned engagement between the segments of the end platesand the adjacent plates, some movement may occur between the end platesand the pack of heat transfer plates. This movement increases as afunction of the distance to the port openings provided on the end plate,where the segments engage the pack of heat transfer plates. By means ofthe sliding element the wear that would otherwise have occurred betweenthe end plates and the neighbouring heat transfer plates can thus beavoided.

Moreover, the sliding element is adapted to engage the neighbouring heattransfer plate, tracing its movements. The sliding element is therebyslideably displaced towards the more wear-resistant end plate.

According to a preferred embodiment, the engagement between the slidingelement and the neighbouring heat transfer plate is achieved by means ofa fixing pattern provided on either or both of the sliding element andthe heat transfer plate.

A further object of the present invention is to provide an end plateadapted to be used according to the plate heat exchanger stated above.The end plate exhibits the general features stated in claim 10,preferred embodiments being defined in appended claims 11–13. The sameadvantages as stated above are obtained by means of an end plate that isdesigned according to these claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present invention will beapparent from the following description of currently preferredembodiments, with reference to the accompanying schematic drawings.

FIG. 1 shows an end plate according to a first embodiment, which isintended to be used in a plate heat exchanger according to the presentinvention.

FIG. 2 shows a heat transfer plate associated with the end plate of FIG.1.

FIG. 3 shows an end plate according to a second embodiment, which isintended to be used in a plate heat exchanger according to the presentinvention.

FIG. 4 shows a heat transfer plate associated with the end plate of FIG.3.

FIG. 5 shows the end plate illustrated in FIG. 3 from the opposite side.

FIG. 6 is a sectional view along the line VI—VI in FIG. 3.

FIG. 7 is a side view of a plate heat exchanger having an end plateaccording to FIG. 3 and heat transfer plates according to FIG. 4.

FIG. 8 is a sectional view along the line VIII—VIII in FIG. 7.

FIG. 9 is an enlarged view of the part A shown in FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS

The end plate shown in FIG. 1 is a frame plate 1 intended to form,together with an additional plate, a “pressure plate” (not shown), themain components of a plate heat exchanger frame. The frame plate 1 isdivided into relatively displaceable segments 10 and each corner thereofis provided with a through port opening 11, connecting pipes 12 beingarranged at said openings. The through port openings 11 and theconnecting pipes 12 allow inflow and outflow of a number of (usuallytwo) heat exchanging fluids in the plate heat exchanger. As shown inFIG. 1, each segment 10 comprises no more than one through port opening11 and a connecting pipe 12 associated therewith. Each separate unitconsisting of segments 10, through port openings 11 and connecting pipes12 is referred to as a connecting module 13. FIG. 1 shows the fourconnecting modules 13 of the frame plate 1.

An elongate central segment 14 is provided at the centre of the frameplate, with two of the connecting modules 13 located on either shortside.

The two end plates included in the frame may both be designed asdescribed above, i.e. both the pressure plate and the frame plate of theframe may be segmented. In this case, the corresponding connectingmodules on the respective pressure and frame plates are interconnected.FIG. 1 illustrates how clamping is achieved by means of clamp bolts 15.At least two bolts 15 are used to hold the respective connecting modules13 together on respectively the pressure plate and the frame plate. Itis preferred, however, to have three or more bolts 15 for each pair ofconnecting modules 13. In addition, a number of bolts 15 are arrangedalong the longitudinal edges of the centre segment 14 to clamp togetherthe centre segments of the frame plate and the pressure plate.

If only one of the two end plates included in the frame is segmented,the segment of one plate is clamped together with the other unsegmentedplate. Bolts may be used here as well.

FIG. 2 shows a heat transfer plate 2 that is intended to be usedtogether with the frame plate 1 shown in FIG. 1. The four corners of theheat transfer plate 2 are provided with through ports 21 a–d. The fourports 21 a–d, a first and a second inlet port 21 a, 21 b and a first anda second outlet port 21 c, 21 d, form together with the ports of theother heat transfer plates a first and a second inlet channel and afirst and a second outlet channel through the plate pack formed by theheat transfer plates 2. The location of the ports 21 a–don the heattransfer plates 2 corresponds to the location of the through portopenings 11 on the frame plate shown in FIG. 1. The channels formedthrough the pack of heat transfer plates 2 communicate with theconnecting pipes 12 of the frame plate 1.

A fluid-tight sealing means 22, for instance a gasket or weld, isprovided on the heat transfer plate 2 and extends round a first inletand outlet port 21 a and 21 b, respectively. A similar sealing means isprovided on every second heat transfer plate of the plate pack. On theintermediate heat transfer plates a sealing means is provided whichextends round a second inlet and outlet port 21 c and 21 d,respectively. Said sealing means contribute to the formation of twoseparate channels extending through the plate heat exchanger, one forthe first heat exchanging fluid and one for the second heat exchangingfluid.

The clamp bolts 15 shown in FIG. 1, which clamp together the two endplates included in the frame, are shown also in FIG. 2. In FIG. 2, thebolts are arranged close to the outer edges of the heat transfer plate2.

FIG. 3 shows a frame plate 3 according to a second embodiment, whichtogether with the pressure plate is intended to form the main componentsof a plate heat exchanger frame. As in the first embodiment, the frameplate 3 comprises relatively displaceable segments 30. However, thepositioning of the through port openings 31 and the connecting pipes 32associated therewith differs from the first embodiment. In the secondembodiment, the through port openings 31 are positioned along thegeometric centre line of the frame plate 3. Thus, four connectingmodules 33, which consist of a segment 30, a through hole 31 and aconnecting pipe 32, are arranged in pairs beneath each other with acentral segment 34 arranged in between. The four connecting modules 33are essentially identical, except for the length of the connecting pipes32. FIG. 3 also shows a first flange 36A arranged adjacent to eachconnecting pipe 32 for connecting the pipes (not shown) through whichthe fluids are fed to the plate heat exchanger.

As in the first embodiment, set bolts 35 hold the respective connectingmodules 33 of the frame and the pressure plates together. The two platesincluded in the frame can be joined, as shown in FIG. 3, by means ofbolted joints 37 arranged round the plate heat exchanger.

FIG. 4 shows an alternative embodiment of a heat transfer plate 4 whichis intended to be used together with the frame plate 3 shown in FIG. 3and which, therefore, has an equivalent appearance. The through ports ofthe heat transfer plate 4, i.e. first inlet and outlet ports 41 a, 41 band second inlet and outlet ports 41 c, 41 d, are arranged along thelongitudinal axis of the heat transfer plate 4 so that their positionscorrespond to the positions of the through port openings 31 on the frameplate 3 shown in FIG. 3.

A fluid-tight sealing means 42, for instance a gasket or weld, extendsround a first inlet and outlet port 41 a and 41 b, respectively. Asdescribed above, similar sealing means are provided on every second heattransfer plate of the plate pack. On the intermediate heat transferplates a sealing means is provided which extends round a second inletand outlet port 41 c and 41 d, respectively. Said sealing means thuscontribute to the formation of two separate channels through the plateheat exchanger, one for the first heat exchanging fluid and one for thesecond heat exchanging fluid.

For engagement between the two end plates of the frame and theintermediate heat transfer plates, a fixing pattern may be provided onthe frame end plates. As shown in FIG. 5, the frame plate 3 illustratedin FIG. 3 has a fixing pattern 38 arranged round the through portopenings 31 and the connecting pipes 32. Thus, the side of the frameplate 3 shown in FIG. 5 is the one that is oriented towards the pack ofheat transfer plates and abuts against the outermost heat transfer plateof the plate pack, the terminal plate. This allows the fixing pattern38, which consists of pressed ridges and troughs, to engage the terminalplate, either the terminal plate itself or, preferably, a correspondingfixing pattern provided thereon. In this manner, each connecting module33 is fixedly attached to the through ports of the terminal plates.

The purpose of said engagement is to obtain a flexibility between theframe and the pack of heat transfer plates as the plate pack issubjected to a length change that is not matched by a correspondingchange in the frame plate and the pressure plate, respectively. Theflexibility is also facilitated by the segmented end plates of theframe.

Naturally, the provision of fixing patterns on the two end plates of theframe and the respective terminal plates may be applied also inconnection with the first embodiment as shown in FIGS. 1 and 2.

FIG. 6 is a sectional view of the frame plate along the line VI—VI inFIG. 3. Two connecting modules 33 are shown having through port openings31 as well as connecting pipes 32. The connecting pipes 32 are ofdifferent lengths and are provided at their free end with a first flange36A. Similarly, the ends of the connecting pipes 32 are provided roundthe port openings 31 of the frame plate 3 with a second flange 36B. Thefirst flanges 36A, connecting pipes 32 and the second flanges 36B arejoined so as to form a unit, preferably by welding, and have similarcorrosion properties.

As stated above, a bolted joint is arranged round the plate heatexchanger to hold together the two end plates of the frame. The forcesgenerated inside the plate heat exchanger are transmitted to the boltedjoint 37 via a first and a second element 39, 40 arranged between thesecond flange 36B and the bolted joint 37.

FIG. 7 is a side view of a plate heat exchanger 7 with the frame plate 3as shown in FIG. 3 and heat transfer plates 4 as shown in FIG. 4. FIG. 7shows more clearly the arrangement of the bolted joint 37 round theplate heat exchanger 7. In addition, FIG. 8 illustrates the semicircularextension of the bolted joint 37 round each of the end plates.

To absorb the wear between the terminal plates and the end plates of theframe, a sliding element 91 is arranged between the pack of heattransfer plates 90 and the end plate, as shown in FIG. 9. The slidingelement 91 engages the outermost heat transfer plate, the terminal endplate 90 a, by means of a fixing pattern provided on the end plate 90 aand/or on the sliding element 91, and is slidingly displaced towards theend plate 3. This means that the end plate 3, which is less sensitive towear, will absorb the wear.

FIG. 9 also shows how the plate pack and the connecting pipe 32 of theend plate are held together by means of a flange 92.

As regards materials, the heat transfer plates preferably consist ofpressed sheet metal whereas the end plates may consist, for example, ofcarbon steel.

It will be appreciated that various modifications of the preferredembodiments described above are possible within the scope of theinvention, as defined by the appended claims. For example, the segmentsof the frame plates shown in FIGS. 1 and 3 may comprise more than oneport opening. In the case where the port openings are positioned closeto each other, it is possible to provide a segment with more than one,suitably two, port openings.

Furthermore, in some cases the end plates and the respective outermostheat transfer plates, the terminal plates, may be separated by anintermediate plate. Thus, direct engagement between the end plates andthe terminal plates is not possible, as described above in connectionwith the fixing pattern of FIG. 5; instead the plates engage via theintermediate plate.

Moreover, engagement between the end plates and the terminalplate/intermediate plate or between the terminal plate and the slidingelement by means of the fixing pattern as described above can be whollyor partly replaced by increased friction between the plates. Theincreased friction may be achieved, for instance, by providing theplates with friction-enhancing surfaces.

1. A plate heat exchanger comprising two end plates, at least one of theend plates being provided with a number of port openings to allow inflowand outflow of a number of heat exchanging fluids, and a number of heattransfer plates located and clamped between the end plates, wherein atleast one of the end plates comprises two separate segments, each ofwhich segments is clamped to the other end plate by clamping means, andwherein the segments are relatively displaceable in the plane of the endplate to which they belong.
 2. A plate heat exchanger according to claim1, wherein each segment comprises a port opening.
 3. A plate heatexchanger according to claim 2, wherein said port openings arepositioned on the end plate along the same geometric center line.
 4. Aplate heat exchanger according to claim 1, wherein a surface withincreased friction is arranged on at least one of the segments of theend plate or on an adjoining plate or on both the end plate and theadjoining plate.
 5. A plate heat exchanger according to claim 4, whereinthe increased friction is achieved by means of a fixing pattern arrangedaround said port opening in one of the segments of the end plate.
 6. Aplate heat exchanger according to claim 5, wherein the plate adjoiningthe end plate is provided with a fixing pattern corresponding to thefixing pattern on the end plate to obtain engagement between them.
 7. Aplate heat exchanger according to claim 6, wherein a sliding element isarranged between the heat transfer plates and the adjoining end plate.8. A plate heat exchanger according to claim 7, wherein the slidingelement is adapted to engage a neighboring heat transfer plate and to beslideably displaced towards the adjoining end plate.
 9. A plate heatexchanger according to claim 8, wherein said engagement of the slidingelement is obtained by means of a fixing pattern provided on either orboth of the sliding element and said heat transfer plate.
 10. A plateheat exchanger according to claim 1, wherein the clamping meanscomprises clamp bolts.
 11. A plate heat exchanger comprising two endplates, at least one of the end plates being provided with a number ofport openings to allow inflow and outflow of a number of heat exchangingfluids, and a number of heat transfer plates located between the endplates, wherein at least one of the end plates comprises two separatesegments that are relatively displaceable in the plane of the end plateand further wherein a surface with increased friction is arranged on atleast one of the segments of the end plate or on both the end plate andthe adjoining plate.